1. Field of the Invention
The present invention relates to a substrate mounting and demounting method implemented by a substrate processing apparatus having an electrostatic chuck that attracts a substrate through electrostatic force.
2. Description of the Related Art
In substrate processing apparatuses, a number of particles may become attached to a rear surface of a wafer as a substrate having been subjected to plasma etching processing. The particles attached to the rear surface of the wafer cause defocusing in a lithography process in which a photoresist coated on a front surface of the wafer is hardened by light.
To cope with this, conventionally, by cleaning the rear surface of the wafer subjected to the plasma etching processing, or by changing the material of a member coming into contact with the rear surface of the wafer in the substrate processing apparatus, a number of particles have been prevented from becoming attached to the rear surface of the wafer before the lithography process.
In the substrate processing apparatus, when the wafer is to be subjected to the plasma etching processing, the wafer is housed in a processing chamber, and mounted on a mounting stage disposed inside the processing chamber. An electrostatic chuck is provided on an upper portion of the mounting stage which comes into contact with the wafer. The electrostatic chuck has therein an electrode plate, and attracts and holds the wafer through an electrostatic force generated by a DC voltage applied to the electrode plate.
Usually, a high DC voltage that generates an electrostatic force is suddenly applied to the electrostatic chuck, the wafer is suddenly attracted to the electrostatic chuck. Thus, there may be cases where the wafer becomes distorted and attracted as it is to the electrostatic chuck, and a stress is generated on a surface of the wafer which contacts the electrostatic chuck (hereafter referred to as “the contact surface of the wafer”) or a surface of the electrostatic chuck which contacts the wafer (hereafter referred to as “the contact surface of the electrostatic chuck”) due to a restoring force of the distorted wafer.
In general, ceramics is thermally sprayed to a surface of the electrostatic chuck, and there are several structurally fragile parts in the surface of the electrostatic chuck. For this reason, the stress generated on the contact surface of the electrostatic chuck breaks the fragile parts, causing particles to be produced, and these particles get stuck in the rear surface of the wafer. Moreover, when the stress generated on the contact surface of the wafer rapidly changes, the wafer may crack.
As an example of a wafer attracting and holding method for preventing the wafer from cracking, a method that gradually increases a DC voltage applied to the electrode plate of the electrostatic chuck has been proposed (see Japanese Laid-Open Patent Publication (Kokai) No. 2001-152335, for example,). This can prevent a stress from rapidly changing, and prevent the wafer from cracking.
However, it is very difficult to remove the particles stuck on the rear surface of the wafer by cleaning. Moreover, as described above, even if the DC voltage applied to the electrode plate of the electrostatic chuck is gradually increased, a stress is generated on the contact surface of the electrostatic chuck as long as the wafer becomes distorted, and as a result, particles cannot be prevented from becoming attached to and getting stuck in the rear surface of the wafer.